1. Field of the Invention
Example embodiments of the present invention relate to a nonvolatile memory device having one resistor and one transistor.
2. Description of the Related Art
Semiconductor memory devices may have a high integration, that is, a large number of memory cells included per unit area, may operate at high speed, and may be driven at low power. Research into such semiconductor memory devices is ongoing and various types of memory devices are under development.
Generally, a semiconductor memory device may include many memory cells connected together. In a dynamic random access memory (DRAM), which is a representative semiconductor memory device, a memory cell may generally be comprised of a switch and a capacitor. DRAMs have several advantages, including high integration and fast operation. However, after being turned off, data stored in DRAMs is lost.
A representative nonvolatile memory device that can conserve stored data even after being turned off is flash memory. Flash memory has a nonvolatile property, in contrast with volatile memory, but may have lower integration and/or may operate slower compared with DRAMs.
Examples of nonvolatile memory devices that are under development include magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), and phase-change random access memory (PRAM).
MRAM stores data using a change in a direction of magnetization occurring in a tunnel junction. FRAM stores data using the polarization of a ferroelectric material. Each has advantages. As described above, memory devices are being developed to increase integration, data retention, and/or operating speed, and be driven with lower power.
PRAM stores data using a change in a resistance value according to a phase variation of a material and may be comprised of a resistor and a switch (transistor). The resistor used in PRAM may be a chalcogenide resistance material, which becomes crystalline or amorphous by controlling a memory device formation temperature. That is, a memory device may be formed based on the principle that resistance of an amorphous resistance material is higher than that of a crystalline resistance material. As described above, when a conventional DRAM manufacturing process is used in the manufacture of a PRAM, etching may be more difficult, and even if etching is performed, the etching process may take more time. A lower etching time reduces productivity and/or increases the unit cost of a product.